No neck glow on Sanyo 20 EZV

dbstallman

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Good evening,

I'm working on a monitor in a friends DK machine and I'm not getting any neck glow.

The fuses are good and I've (not related to this issue) installed a complete cap kit on it and the audio board. I'm getting about 1.7 volts at TP 91, and ~150 volts on both sides of the 300ma DC fuse.

The Q901 transistor shows 150 volts on the collector and 0 or 1.5 volts on the base and emitter. All of the diodes (D601-604) are good when tested off the chassis.

Does that mean IC601 is my next suspect? If so, where is the best place to get one?

Thanks,
Brian.
 
i would reflow the chassis all over. especially around IC601 and all the large resistors.

i had one like that once and i hit about every solder joint in those areas and it came back to life.

also what is your B+ on test point BJ on the chassis.
108 vdc is your target.

Peace
Buffett
 
I'll give it a shot.

I also forgot to mention, I replaced Q901 when I was trying to figure the problem out. Obviously it made no difference in the readings.

Brian.
 
I reflowed the half of the board that has voltage regulator circuit and IC601. Nothing has changed, unfortunately.

The B+ voltalge at BJ is 1.8 volts. That is the same value as I have at the base and emitter on Q901. I also noticed the resistor at R609 is hot enough to melt the plastic on my test leads (also gave me a small amount of anonymity when I burned the fingerprint off my left index finger :O).

Brian.

i would reflow the chassis all over. especially around IC601 and all the large resistors.

i had one like that once and i hit about every solder joint in those areas and it came back to life.

also what is your B+ on test point BJ on the chassis.
108 vdc is your target.

Peace
Buffett
 
you need to find out what is shorted and drawing to much current thru that resister.

start measuring everything before and after the resistor.

and just in case look for bridged solder joints.

Peace
Buffett
 
sanyo

turn your chassis over. with a maginifier, check all the traces.broken traces on these chassis are very common. especialy near the flyback.
 
I spent about an hour going over the entire board with my lighted magnifier arm. I found a couple of spots where pads were lifting off of the PCB, but they were still making good contact. I went ahead and secured them back down and reflowed the solder on those contacts. I also found a couple of points where the bend pins from resistors looked to be really close, so I lifted them farther away (they weren't making contact, but better safe).

On a whim, I decided to check the HOT and found that it was shorted. I'm going to get one and replace it now. My question now is, how is it that my AC fuse was still good with a blown HOT?

Brian.
 
It's still good, although it is a 1A instead of a 300mA. I've not had the monitor powered for more that 2 minutes at a time, but I've done that at least a dozen times and it hasn't popped.

My HOT reads 0.001 or 0.002 on the diode check in both directions from pin to pin or case to either pin, so that is blown per my understanding.

Brian.

check the small fuse on the chassis.
when the H.O.T blows it takes that fuse out with it.


Peace
Buffett
 
black lead to the case and red lead to either pin.

with the readings you posted it is shorted.

and put the correct fuse in there the 1a is way too high.

Peace
Buffett
 
OK,

I replaced the H.O.T. and put a 315mA fuse in and powered it up.... progress! The neck glowed for about a second and then the fuse blew.

I rechecked the H.O.T. and it is good, I pulled the end of J27 per Sanyo's flowchart and found the resistance from TP91 to ground to be ~12.5k ohm...

I'm still reading ~150v on the collector of Q901, but the base and emitter are now at ~9v. The same is true of TP91 when powered up... Obviously, the big resistor has stopped heating up since the fuse going to it has blown.

Where should I look on the flyback to see if it is leaking? I know the focus and screen pots aren't on the flyback so I won't see anything there... Or is this probably not the flyback?

Brian.
 
sanyo

When those pads lift, they are no longer any good.. You need to solder a wire from the lifted side to the next contact point or just to the trace itself.. These will appear to be good per the meter, but when power is applied, they wont hold.this has happened to me.
 
They lifted at the end of a run. The next contact trace was what was holding it in place. I can try reinforcing it, but the traces are still intact. If it continued beyond the lifted point I would not have put it back down, I would have just replaced the trace like you said. This isn't my first trip to the rodeo :p

Brian.

When those pads lift, they are no longer any good.. You need to solder a wire from the lifted side to the next contact point or just to the trace itself.. These will appear to be good per the meter, but when power is applied, they wont hold.this has happened to me.
 
They lifted at the end of a run. The next contact trace was what was holding it in place. I can try reinforcing it, but the traces are still intact. If it continued beyond the lifted point I would not have put it back down, I would have just replaced the trace like you said. This isn't my first trip to the rodeo :p

Brian.

my apology... ride on cowboy!!!
 
my apology... ride on cowboy!!!

Love that reply! Thanks for your help so far, peerless, you gave me the nudge to find the blown hot.

I have now found that R609 is cracked (I don't know if it was cracked when running hot before, but it is actually split open now). I haven't powered up the monitor since it blew the fuse.

I'm going to replace it now, but would that damaged power resistor indicate that my flyback is gone? Is it a symptom or cause of more damage?

Brian.

Edit : Hmmmm... maybe this isn't my problem. I pulled it and measured 180 ohms across it. I doesn't appear to be damaged other than an open crack on the side (which a good squeeze closed right up). I also tested all the caps for shorts, none found.
 
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resitors

one thing that i do is heat the resistor up with the iron and see if it holds within tolerance.ive found a couple of bad ones this way.
 
Ok, I'm still stumped...

I thought that the flyback was the only thing that could be causing my DC fuse to blow (after I replaced the H.O.T.). Unfortunately after putting in a new flyback from Bob Roberts, I am seeing the exact same behavior: The neck glows for almost a second and then the fuse blows.

Does anyone have any other ideas? I'm still getting ~160V at the collector of Q901 and the voltage at TP91 is ~8V... None of the flowcharts I've looked at have an answer for either of those levels. :(

Brian.
 
voltage

whats your voltage at both fuses? and ac input. also , are you sure the hot is good?
 
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The H.O.T. in there right now is brand new, and it tested good before I installed it and I have tested it tonight and it is still reading correctly.

The input voltage is 120VAC (I guess I was wrong about the voltage on that outlet in my Tecomo candy cab). Voltage at the AC fuse is 120, and at the DC fuse (the end that has voltage since it is blown) is 160VDC.

Brian.

whats your voltage at both fuses? and ac input. also , are you sure the hot is good?
 
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